Radio distance and direction indicator



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INVENToR. .L U/s um L VA REZ BY /'M/ZYAM M ug. 30, 1949. l.. w. ALVAREZ RADIO DISTANCE AND DIRECTION INDICATOR llsheets-sheet 1o Filed June 27, 1944 Aug. 30, 1949. w. ALVAREZ RADIO DISTANCE AND DIRECTION INDICATOR Filed June 27, 1944 11 Sheets-Sheet l1 SQUARING CIRCU/ T INVERTER CIRCUIT' INI/ER TER LINEAR SWEEP a :NERA ron sauna/Nc 7.2 c/pcu/ r PR OPOTON L T0 GROUND SPEED ANTENNA SYSTEMv INVENTOR.

LU/SW. ALVAREZ BY QM Wlan/fl COMPUTER FIG-39 zx Po TENT/alunne@ @0% scA/v CAMS s Moron Patented Aug. 30, 1949 RADI DISTANCE ANID DIRECTION INDICATOR Application June 27, 1944, Serial No. 542,287 27 Claims. (Cl. 343-7) i Introduction This invention relates to a communication system and more particularly to a system for presenting in panoramic form the location and disposition of objects as they might be seen [rom the air. In particular, the system hereinafter described is a radar or radio echo detection system presenting objects and targets principally on the ground lying in thekpath of flight of an airplane.

A system of this character has great utility both in war and in peace. Thus for war purposes, a system of this character may be used for aiding in the approach toward and the release of bombs on desired targets.` For peaceful purposes, a system of this character may nd application as an aid to navigation of planes under conditions of poor visibility. Other uses for a system of this character may be provided as the full utility of the system is apparent.

There are at present in use radar systems on ground equipment which systems are adapted to present a sort of map of the territory around the system. As a rule. such systems in their simplest form comprise a highly directional antenna system to which a transmitter and receiver are alternately coupled. The target presentation is made on the screen of a cathode ray tube and generally consists of a series of radial sweeps from the center of the screen'. The azimuth is generally correlated with the angle of the sweep with respect to a fixed radial direction, While the range is a function of the radial distance from the center of the screen.

In airborne equipment, however, the problem of panoramic presentation involves quite a number of different objectives. Thus, for example, the view ahead with respect to the line of travel of the plane is of immediate concern, while the desired View across the line of travel generally increases as the distance from the plane lncreases. As a rule, the terrain over which the plane has already passed is of no concern, and this is also true of the terrain transversely on either side of and below the plane. I

Because the range of vision increases quite rapidly with altitude, it is clear that in a plane the range of distant targets may increase quite rapidly as the altitude of the plane itself increases. Due to the nature of the general problem, of which more Will be stated later, a. sector panoramic presentation of the ground for a plane is beset with numerous special problems requiring special solutions.

movement;

the United States of 2 Drawings In the drawings:

Fig. 1 is a diagram illustrating the geometrical principles involved in the invention;

Fig. 2 is a diagram od of presentation of information on the screen of a cathode ray tube;

Fig. 3 is a diagrammatic showing of the antenna system together with the scanning motor;

Fig. 4 is an isometric view of the connecting block in the antenna system;

Fig. 5 is an elevation detail of the reecting member used in the connecting block of Fig. 4;

Fig. 6 is a sectional elevation of an antenna system;

Fig. 'l is an elevation view antenna system of Fig. 6;

Fig. 8 is an isometric view of one of the dipole elements;

Fig. 9 is a sectional plan view looking down upon the antenna and showing the transition section between iixed and adjustable wave guides;

Fig. 10 is a sectional plan view of a modied form of transition section;

Fig. 11 is an end elevation taken on line iI-ll of Fig. 1G and showing the coupling portion of the xed wave guide;

Fig. 12 is a diagrammatic view partly in blocks of a simple system for illustrating the invention;

y Fig. 13 is a diagrammatic view partly in blocks and partly in wiring detail explanatory of the blocks of Fig. 12;

Fig. 14 is a wiring diagram' of one form of a voltage combining lcircuit which may be used in the system of Fig. 12;

p Figs. 15 and 16 are geometrical diagrams relating to the introduction of correction for roll and yaw, respectively;

Fig. 17 is a. circuit diagram, partly in block form, illustrating one method of accomplishing corrections for roll and yaw;

Fig. 18 is a schematic showing of a screen of a cathode ray tube for the purpose of illustrating the effect of compensation for the forward from the rear of the Fig. 19 is a view of the screen of a cathode ray tube illustrating one way of providing stabilization of indication against jinking maneuvers;

Fig. 20 is a diagram illustrating certain conditions of the problem of bombing a target from an aircraft;

Fig. 2l is a block diagram of apparatus for obtaining the release time for bombing a target with the help of the present invention;

illustrating a suitable meth- Fig. 22 is a block4 diagram of another form of apparatus for obtaining the course and release time for bombing the target with the help of the present invention;

Fig. 23 is a block diagram of one arrangement of computer apparatus for stabilizing indications on a map-making cathode ray tube when an aircraft is engaged in maneuvers involving changes of course;

Fig. 24 is a view of the indicator of a cathode ray tube illustrating the presentation of an aiming point or virtual target marker;

Fig. 25 is a block diagram of a computer and release apparatus adapted to cooperate with apparatus providing indications of the type shown in Fig. 24; y

Fig. 26 is a. block diagram of one form of apparatus which includes an auxiliary cathode ray tube providing an expanded view of a portion of the terrain scanned;

Figs. 2'7, 28, 29, 32, 34, 35 and 36A are diagrams of specific circuits which are of particular utility in connection with this invention;

Figs. 30 and 31 are diagrams relating to the operation of the circuit of Fig. 29;

Fig. 33 is a diagram relating to the operation of the circuits of Figs. 32 and 34;

Fig. 36 is a diagram relating to the operation of the circuit of Fig. 35;

Fig. 37 is a block diagram of a computing system, including certain features of Fig. 23;

Fig. 38 shows the screen of a cathode ray tube with indications provided by the computing system of Fig. 37; and

Fig. 39 is a block diagram of a complete, compensated system with computer.

Fundamental geometry f` problem A preliminary and simplified system and accompanying problem will first be discussed. In this the assumption will be made that the plane maintains its desired direction and level substantially as might be expected under good flying conditions where no problem of drift, rolling, yawing and jinking or sudden changes to avoid other craft or anti-aircraft fire are taken into account.

Referring first to Fig. 1, let I represent a transverse element of an airplane with the direction of ight actually perpendicular to this line. At any instant t=0, let a rectangular coordinate system be assumed with the origin 0 being on the face of the earth directly below the airplane.

In order to simplify the entire problem, the assumption will be made that the surface of the earthis flat. In practice, simplification of the apparatus tends to compensate in some manner for this assumption so that a substantially accurate presentation is possible assuming that the ground does not have any sharp projections, such as hills or mountains, or declivities, such as chasms or valleys. Such irregularities have characteristic indications Whose nature is obvious to a trained operator.

With O as origin, let XX be a coordinate axis transverse to the line of night of element I and lying within the assumed flat plane of the earth's surface. Similarly, let YY be the other coordinate axis along the direction of flight of plane, the airplane containing element I.

The proper operation of a radio echo detection system requires that the radiant energy issuing from and arriving at the antenna be concentrated. For reasons which will be apparent later in connection with the geometry of the problem,

the radiant beam is formed as a thin sheet. The antenna system, which will be described in detail later, has the characteristic of initially (i. e. without reflectors) generating a generally conical sheet of radiant energy. The axis of the cone lies along line I.

At one extreme of the transverse sweep, the conical radiation extend-s toward X and may have a certain predetermined minimum angle at the tip of the cone. This minimum angle may be determined by various design considerations. 'I'he intersection of this cone of radiant energy with the assumed fiat surface of the earth results in a hyperbola. In fact, as is well known, the intersection of the cone of radiation with the surface of the earth would result in a hyperbola even if line I were not parallel to the earths surface, as long as the angle between I and the surface of the earth was less than the half angle at the cone tip.

The hyperbola formed as above and partly shown in the drawing as one of a series of dotted arcs, may thus be considered a curvilinear element of ground upon which a range scanning cycle is to be performed. Assuming that a range scanning action results in the progressive presentation of target echoes reflected along a hyperbolic arc, the angle of the cone may be increased. This vvariation of cone angle may be continuous and if s0 must be slow with relation to the range scanning speed along any one hyperbolic arc.

As the cone angle becomes larger, the line oi intersection between the cone of radiant energy and the surface of the earth approaches line YY. Finally the cone angle becomes at which the height of the cone decreases to zero and the cone is merely a at plane going through YY' and perpendicular to XX. The line of intersection is naturally YY. As the antenna scanning action progresses, the plane is distorted to a cone on the X side of the YY plane and decreases in angle until finally a minimum angle cone is generated. Thus successive hyperbolic arcs are generated. While the drawing shows separate arcs are generated. While the drawing shows intersecting curves, it is understood that with a slow, continuous transverse sweep the actual variation of the cone is continuous even though slow so that an infinite number of arcs are actually generated.

As an example of the relative values of scanning along a hyperbolic are of intersection and the movement of the arc to or from YY', the following may be given. 'I'hus along an arc, range scanning may be effected at the rate of between 500 and 2,000 times per second, this depending upon the maximum range of the system, power, etc. The conical sheet of radiation may go through from one extreme position on the X' side to the other extreme position on the X side to form a half cycle of transverse scanning in something like 1/3 or 1/2 a second. In practice, by limiting the angle of transverse scan along XX' to about 30 on each side of the origin, it has been found that the movement of the arc of intersection is small compared to the speed of range scanning along an arc. Y

In this connection, the angular thickness of the sheet of radiation as seen from the airplane becomes important. As applied to the drawing, the thickness of the conical sheet would determine the width of the so-called line outlining a hyperbolic arc. Naturally it is impossible to generate a conical sheet of radiation without having a result, the thicker the sheet of radiant energy,

the faster the scanning angle may be varied. In the example given above.` it is possible to obtain a sheet of radiant energy having an angular extent of something of` the order of about 1. Hence it is important that range scanning along the 'arc of intersection be suiliciently rapid with reference to transverse scanning so that thorough, over-all scanning is eiected.

As far as utility is concerned, scanning of the ground behind the plane, i. e. on the right of XX', is unnecessary. Thus the antenna system may be provided with suitable reflectors so that no scanning is eiected in this region. In addition, scanning of the ground along the axis XX is only necessary for a comparatively short angular range as viewed from the plane. As is evident from the curvature of the hyperbolic arcs, a scanning angle of about 30 from each side of the vertical along the XX axis results in a substantial coverage when projected forward along the line of travel of the plane.

Assume for'the sake of example that at any particular instant of time, the cone of radiation from line l is such that it extends to the right of the plane and Aintersects the earth along the solid line shown. Let P be the location of any point to be scanned at a particular instant, this point moving along the hyperbolic arc (shown in full line) representing the line of intersection between the cone of radiant energy and the assumed flat surface of the earth. B is the point on theX axis at which the hyperbolic are containing P intersects it. Since the axis of the cone of radiation is line l, parallel to XX and directly overhead, it follows that angle a formed by the intersection of lines OA and AB will be the complement of the half angle of the cone. In other words,

- as shown here, the cone axis is line l prolonged,

be drawn.

Referring again to point P, it is important that its coordinates with reference to origin O be provided in the airplane. Angle a and slant range AP are directly observable quantities but of no intrinsic value for map making. In order to get the :c and y coordinates at point P, let h be OA, the altitude of the plane, and r be AP, the slant range. The ,ze coordinate of point P becomes r sin a. This is evident if geometric lplane passing through line AP and parallel to the X axis is imagined. Such a plane will pass through the axis of the cone of which the sheet of radiation forms part, Considering the above plane, the intersection thereof with the YY' axis will give the y coordinate of point P and this turns out to be the \/12h2.1:z, in which :z: is the X coordinate of point P.

In the above values of the coordinates of point P, it should be noted that a, the angle of scan, varies quite slowly, i. e. may go through its complete cycle of valuesin between and 1 second of time. h, the altitude, is practically constant or may vary slowly with relation to the speed of operation ofthe entire system and, in any event, is a denitely determinable quantity. The slant range r varies very rapidly going from its minimum value h up to a maximum value in a small fraction of a second, this being a function of the pulse repetition frequency.

It is thus evident that the operation of the system will be facilitated by providing sweeps across the face of the cathode ray tube which will at any instant delineate, on a reduced scale, the hyperbolic arcs representing the intersection of the sheet of conical radiation and the ground. This is shown in Fig. 2, corresponding lines and points being similarly indicated. It is understood that the hyperbolic arcs delineating the path of the sweep are not actually visible, as a rule, and that the system may be so adjusted that only targets having certain reection characteristics will show up. For each hyperbolic sweep, the a: component of the instantaneous position of the beam on the screen of the tube will, as previously pointed out, be given by the expression r sin a. For all practical purposes, a may be considered constant during the time of one hyperbolic sweep, although slowly varying from one such sweep to another such sweep. r itself, is a function of time rather than geometry, and is a parameter ordinarily taken care of by the fact that the instantaneous position vof the beam on the screen is from the nature of things directly connected with the magnitude of 1'. Thus the a: component of the sweep in a simple modification of the system may be a substantially normal saw-tooth generator wherein the steepness of the voltage rise is varied as a changes.

The y coordinate of the beam is the same as the y coordinate for point P. Thus the sweep for determining the y position of the beam will not be a linear function.

The a: coordinate may have positive or negative values and this will be taken care of in the cathode ray tube by reversing polarities. The 'y coordinate need only be positive.

It is clear from Figs. 1 and 2 that as the hyperbolic arcs approach XX', there is a tendency for the arcs to be concentrated. This indicates that the resolution of the echo detection system is a minimum for ground directly below the plane. This is due to the slow rate of change of the slant range with respect to other linear dimensions for the region around origin O.

Inasmuch as the terrain directly below is of no great interest. it may be eliminated from the in` dicating screen by creating an artificial lower limit 5 for vertical beam travel. This may be accomplished by suitable gates and voltage biases.

The antenna system tion pattern of the dipole system would be de termined by the spacing between dipoles in terms` of wave lengths. With a full wave length spacing. the radiation would be outwardly in a generally iiat plane, assuming, oi course, that the Wave guide is straight. By varying the effective spacing in terms of the wave length between dipoles, the sheet of radiant energy is emitted in the form of a conical surface with the axis of the cone substantially coincident with the alined dipole arms. The greater the variation in eective spacing from a wave length, the narrower (at the cone tip) the conical beam of radiation will be. 'I'he conical nature of the sheet of radiation is due to interference patterns, as is well understood in the art.

It has been found that if the dipoles are arranged a lwave length (as measured in the wave guide) apart, all dipoles being similarly arranged, the pattern of radiation includes objectionable side lobes. To overcome this, the system has dipoles spaced at half wave intervals (as measured in the wave guide) with adjacent dipoles being reversed in polarity. Thus the dipoles are all in phase at half Wave length spacing. The resulting pattern is sharp and has substantially no side lobes.

While various means may be utilized for varying the effective spacing between adjacent dipoles, it is preferred to accomplish this by maintaining the dipoles relatively fixed and varying the phase velocity of the energy through the wave guide. This may be accomplished in a simple manner by varying the long dimension of the guide (the b side). This variation in guide dimension may be controlled by suitable motor-driven means so that a transverse scanning action is effected. In the system disclosed herein, the wave guide system is actually susceptible to feed from either end. Hence by feeding thewave guide from one end and going through a scanning cycle and then feeding through the other end and repeating the scanning cycle, a complete scanning over the entire transverse range of the system is possible.

Referring particularly to Figs. 3 to 5, a wave guide I is shown upon which a series of alined dipoles II are mounted. Wave guide I0 may have small side sections I2 and I3 and elongated portions I and I5 forming a generally closed system. Wave guide portions I 4 and I5 are preferably coupled together by means oi a suitable coupling block I6 which in its simplest form merely consists of a generally cube-shaped member having wave guide channels I1 and I8 intersecting at right angles to form a region I9 within the block. The block itself may be of any suitable material such as copper or brass and may be made in any suitable fashion, such as in two parts as shown in Fig. 4.

Wave guide sections I4 and I5 are adapted to fit on opposite sides of block I6 and may be coupled thereto by choke coupling members 20 and 2I described and claimed in detail in the copending application of Winfield W. Salisbury, Serial No. 489,844 filed June 5, 1943 issued October 19, 1948 as Patent No. 2,451,876. In general such choke sections utilize a half wave length distance between the edges of the wave guide proper and end of slot forming a metallic short. The other wave guide section in the block may have a feed section 23 for supplying high frequency to the system and a terminal energy absorbing section 24 having suitable material therein packed for absorbing radiant energy. Material 24 may be of some high resistance material such as carbon particles or sawdust, and is generally 8 disposed in such -a manner as to provide a, tapering or slant surface 23, as shown.

Disposed within region I9 is a high frequency reflecting member 21. In its simplest form this may consist of a lo'op of metal, such as copper. adapted to have the desired dimensions for resonating to the frequency supplied by wave guide section 23. Instead of a loop, 21 may be a solid sheet of metal having suitable physical dimensions. Reflector 21 may have bearing pins 28 and 29 journaled in a suitable apertures in block I6 so that reflector 21 may operate in planes perpendicular to the short or a side of the wave guide. This reiiector is adapted to assume one of two positions, as shown in Fig. 3, so that high frequency energy supplied by 4glide section 23 may be reected into wave guidi.a 'section Il, as shown, or into wave guide section I5 when the reflector is in the dotted line position.

Reector 21 has the property of not only acting upon the main incident energy supplied from wave guide section 23 but also acting upon the energy that has already passed through the radiating system proper. Thus, as shown in full lines, reflector 21 operates on energy coming into guide section 23 by diverting it to wave guide I 4 and thence through wave guide section I2 and I0. Whatever energy remains after having passed through the length of section I0, continues on to wave guide section I3 and then I5 and is then reected by member 21 into absorbing material 24. Thus material 2l merely functions as a load for absorbing undesired energy, it being essential that radiation from member 24 back to refleeting loop 21 be reduced to a minimum. Actually, because of the comparatively small amount of energy left to be handled by material 24, some reflection maybe tolerated without undue harm.

Reflecting member 21 may occupy either one of the two positions shown. It is highly desirable that reflecting member 21 should never be in a plane perpendicular to the axis of feed guide 23. In this position, substantially total reflection back into the oscillator portion of the transmitter will occur. This has an adverse effect on the stability of the oscillator particularly if a magnetron is used. To avoid this difliculty, reector 21 is oscillated back and forth from one position to another and back again without going through the objectionable position referred to above.

A simple form for obtaining this movement is shown diagrammatically. Thus reflecting member 21 may have a driving rod30 coupled to a cross-shaped member 3l. Cross-shaped member 3i is adapted to be moved by pins 32 and 32a carried by gears 33 and 33a driven by a suitable motor 36. Gears 33 and 33a are driven through a gear 33h at half motor speed (for timing in relation to other motor driven parts). It'is clear that by virtue of this movement reflector 21 may be timed so that it will be quickly moved back and forth over a range and then left undisturbed during a scanning operation until the necessity for moving again arises.

Variable wave guide section I0 is shown in detail in Figs. 6 and '7. The view in Fig. 6 is a section transverse to the length of the wave guide. In practice, the entire structure may have a length of the order of between 10 and 20 feet and is preferably mounted transversely in an airplane so that under normal flying conditions the antenna system has an unobstructed view over the entire range to be scanned. The mounting of the system may be carried out in any approved manner and the antenna system itself may be disposed either in the leading edge of a regular or special Wing section or any other desired portion. In practice, the antenna system will be enclosed in a suitable housing so shaped as to provide substantially unimpeded transmission of radiant energy. Such a housing may be made of Plexiglas and may if desired be double-walled and constructed in accordance with the principles disclosed in the copending application of Thomas J. Keary, filed May 18, 1944, Serial No. 536,142.l The space between the housing walls may be traversed by heated air to prevent condensation or ice formation, all of which would have a deleterious action upon radiation characteristics. The antenna system proper, Fig. 6, consists of a suitable metal body 36 having an intermediate wall section 31 with side arm sections 38 and 39. This may be formed of any suitable metal such as aluminum or steel for structural strength or brass'. Intermediate portion 31 is normally vertical when the plane is flying level and the antenna system properly adjusted. This intermediate portion has a central strip 40 constituting the wide side of a wave guide. Central strip 40 is bounded, at one side, in this instance the bottom side, by a flange 4I having a slot 42 therein. Flange 4l preferably is high enough so that it is suitable for use as the small or a side of the wave guide. It is understood that in the event of central section 31 being made of steel or other material having poor conductivity that a suitable lm of good conductive material such as copper will be disposed along the portion dening Wave guide section 40 as well as flange 4| and also a region above 40 which will be explained later.

Cooperating with wave guide strip 40 is a wave guide bounding block 43 having a flanged portion 44 suitably slotted at 45. Movable block 43 is supported in the manner shown so that a strip 46 is opposed to guide strip 4B, whileiiange 44 opposes flange 4I. Movable block 43 is supported in such a manner that flanges 4l and 44, respectively, have small clearances 41 and 48 between moving and stationary parts. These clearances are exaggerated in the drawing and in practice will be something of the order of several thousandths of an inch. The dimensions of the C,

flanges, clearances and slots 42 and 45 are such that a choking action results in accordance with the principles disclosed in the previously mentioned application of Winfield W. Salisbury. In general the slot depth is close to a quarter wave length while the distance of slot from wave guide edge is about a quarter wave length. Some compromise and testing is necessary, particularly for rectangular guides. Ihus high frequency energy within the Wave guide region bounded by surfaces 40 and 46 and flanges 42 and 44 will be conlined to this region without any substantial loss by radiation even though metallic discontinuity around the perimeter of the section is present.

The showing of the support of movable member 43 is diagrammatic and in practice means will be provided for maintaining this member in alined, parallel relationship to wall section 31. It is understood that member 43 is moved transversely to its length, i. e. up and down as seen in Fig. 6. To this end, member 43 may have at spaced intervals throughout its length eye sections 50 through which a bolt Jpasses and engages a link 52. A forked link 53 is pivotally mounted as shown in the drawing to operate from side portion 38 and this link together with link 52 are connected together by a pivot bolt 55 to form a toggle link. It is understood that this toggle arrangement is repeated at suitable intervals through the length of the antenna system. Running the entire length of the antenna system is a drawbar 56 engaged by pivot bolt 55 so that the toggle may either be opened or closed. It is clear that if drawbar 56 is moved along its length that there will be a tendency for the toggles to move member 43up or down and thus vary the long dimension oi the wave guide.

Referring back to Fig. 3, drawbar 56 may be actuated from a cam follower 51 riding in a cam 58 of a disk 59 suitably rotated by motor 34. The shape of cam 58, as well as the characteristics of the entire linkage system, are such that the variation of wave guide dimension results in a scanning action from the antenna system whose variation with respect to time is substantially uniform. The actual rate of variation of guide dimension with respect to time mayV be irregular and must be engineered to correspond with the characteristics of the entire antenna system. This, of course, is a matter within the scope of anyone skilled in the art.

Antenna member 31 carries throughout its length, as indicated in Fig. 3, a series of dipoles l I, one of which is shown in detail in Fig. 8. As shown in Fig. 6, body portion 31 along Wave guide strip 30 is provided with suitable apertures into which the individual dipole assemblies are mounted. The dipoles may be secured in any suitable manner either by threading into wall 3l or by a press t or by soldering and are spaced a half wave length apart with reference to the wave guide interior.

Each dipole assembly, as shown in Fig. 8, comprises a short section of coaxial cable having an outer conductor 55 and an inner conductor 56. These two may be made of any suitable metal such as brass. Outer conductor 55 mayhave one end 51 reduced only as far as the outer surface is concerned, it being understood that the inner surface of outer conductor 55 is a substantially smooth cylinder. Outer conductor 55 has the other free end slotted longitudinallyat 58 and 5S, these two slots being diametrically opposed and so proportioned as regards depth and width as to constitute a choke section `of that portion of the outer conductor containing slots 5E and 59. Rigidly carried by outer conductor 55 at the slotted ends thereof are the dipole elements proper consisting of fingers i60 and 6l.

As is evident from Fig. 8, ngers 60 and 6l are in line and perpendicular to the plane of slots 58 and 59. One of the dipole ngers such as 60 stops at outer conductor 55, while the other finger 6l passes through outer conductor wall 55 to engage inner conductor 55. By virtue of the choking action of slots 58 and 59 in the dipole assembly, finger 60 is eiectively energized by outer conductor 55, while linger 6| is eiectively energized by inner conductor 56. It is understood that the various parts of the dipole assembly are suitably proportioned for the frequency to be used.

As shown in Fig. 6, the dipole assemblies are mounted in alined relationship with outer conductor 55 normal to Wall section 31 and ngers 60 and 6| alined along the length of the antenna system. It is understood that adjacent dipole assemblies have reversed positions with regard to polarity. In other words, it is understood that finger 60 of alternate ones of the dipole assem-v il blies will always be on the corresponding side f vhe entire dipole assembly. Inner conductor 56 constitutes a probe which is inserted to a predetermined depth into the variable width wave guide.

In order to direct the energy, wall section 31 carries a pair of metallic reectors 63 and 64 above and below the alined dipoles. Reflector |63 below the dipole assembly may merely be a -at sheet, as shown, while reector 64 may have a curved lip 65 at the top. The angle between reectors -63 and 64, as well as the dimensions of the reflectors and the design of lip section 65. are such as to produce a reection characteristic pattern generally known -as co-secant squared. Such a pattern as viewed in the plane of the paper of Fig. 6, will direct the least amount of energy downward, i. e. vertically down as seen in Fig. 6, with the amount of energy increasing in accordance with the square of the angle going up to a. horizontal position. The ex-act pattern does not necessarily have to follow the secant squared law. By suitable proportion of the reflector members a desirable pattern of radiation may be obtained. Thus as disclosed here, the radiation from the antenna system if str-aight ahead along YY of Fig. l will be a minimum directly below to point O and increase along Y'. This is highly-desirable since the slant range increases and thus requires more power to be radiated from the antenna system for target echoes of satisfactory intensity. For other scanning angles where the beam would lie along a curved, hyperbolic arc, the intensity Will vary generally in accordance with the square of the Y ordinate.

The spacing of dipole assemblies Il from each other is fixed at a half wave length as far as geometry is concerned. The dimension of the movable wave guide is chosen to obtain the half wave length at a desired point in its travel. As the variable wave guide changes its dimension, the effective phase angle between adjacent dipoles varies. Thus it may be provided that when the wave guide has its maximum width, i. e. when movable member 43 in Fig. 6 is in its highest position, the direction of ypropagation from the entire assembly is either straight ahead in the form of a fiat sheet of radiation or preferably slightly cocked to one side, the sheet then having a slight curvature corresponding to a conical sheet of radiation with a very wide angle. As movable member 43 travels downwardly as seen in Fig. 6, the sheet of radiation if cocked to one side, for example the right side, will go through the straight ahead position where the sheet of radiation is a flat plane and then be bent into a conical sector sheet until finally the maximum scan angle is attained. This corresponds, of course, to the bottom position of movable member 43 with the wave guide having its smallest a dimension. It is understood that when the term conical sheet of radiation is used that this is merely a simplication and assumes radiation from the dipole system without disturbance of the pattern due to reflectors or the supporting structure. Actually the radiation is in the form of a part or sector of a conical surface.

As has been previously pointed out, the maximum angle of scan may be any desired angle such as 30. When this maximum angle has been reached, movable member 43 then begins to reverse its direction of travel and go upwardly so that the angle of scan begins to decrease. When movable member 43 has reached its top position, the angle of scan will have gone through its enl2 tire range, for example, -1 through zero to +30a then back again to zero and to -1. One side may be considered positive and the other side negative. In this position, reecting member 21 in the antenna system is suddenly turned so that the 1 scan angle is changed to a +l scan angle and the entire scanning cycle continues from +1 to zero to 30 back again to zero to +1". Thereupon renector 21 is again turned and the entire cycle of scanning is repeated. By thus providing a sort of scanning toe-in, danger of a blind spot in front is eliminated. In fact, this double scanning of the 1 arc on each side of the straight ahead direction may be used for calibrating the system. Thus an object straight ahead should appear as one object on the screen if the sweeps and system are properly calibrated. In case of improper calibration, it is evident that an aberration will result, and the object may appear` to be duplicated.

The location of the line of dipoles with reference to the wide side of the guide is a matter of experiment and over a certain range is not critical. Theoretically, the maximum intensity of radiation would be obtained if the dipoles were always in the center of the long side of the wave guide as this dimension varied. .The practical realization of such a structure would involve complex mechanism of doubtful practical value. Ordinarily in a wave guide having no probes therein the electric vector magnitude varies generally sinusoidally with respect to the long side of the wave guide, the maximum intensity of the vector being at the center with zero intensity at the ends. The presence of the dipoles and probes tends to distort this sinusoidal distribution and generally tends to peak the curve toward the probe. Hence even when the probe is not atthe center of Wave guide section 40 as would be the case when member 43 moves, there is a tendency for the electric vector to be pulled toward the probes so that the asymmetric location of the line of probes 56 in the wave guide is compensated for. In practice, the dipoles may be disposed in the center of the wave guide determined by movable member 43 when it is somewhat short of its highest position. This, however, may be varied in a manner determined by the operating characteristics of the system.

It is clear that between Wave guide Ill having a variable dimension and the rest of the wave guide system shown in Fig. 3, there will have to be a transition section approximately at points 63 and 64 shown in Fig. 3. Such transition sections are shown in Figs. 9 and l0. Referring first to Fig. 9, movable member 43 of variable wave guide portion may have at each end thereof a link 65 engaging a pivoted wave guide section 66. Pivoted wave guide section 66 is generally similar in structure to movable member 43 with the exception that section 66 is pivotally mounted at 61. At 61 wave guide section 66 merely turns and has very little if any motion with respect to the xed wave guide 68. Pivoted section 66 may thus move around pin 61 as shown in dotted lines. As is true of movable section 43, pivoted section 66 is also provided with a choking slot 10. By suitable design of the various choking slots, leakage of energy between guide sections 43 and 66 may be reduced to a nominal figure. In fact, if desired, the opposing faces of these two wave guide sections may be suitably shaped so that one may rock on the other and thus provide for practically minimum 76 clearance.

Another form of transition joint is shown in Figs. 10 and 11. In Fig. 10, movable member 43 cooperates with fixed flange M as shown in Fig. 6. This section is taken through an intermediate portion of the wave guide parallel to the long side. Referring again to Fig. 10, fixed flange 4| has a slot 'Il formed in the end thereof, as shown, this slot having its short dimension extending transversely of the fiange toward choke slot 42 and its long dimension longitudinally of the flange or parallel to slot 42. The dimensions of slot 'Il depend upon the frequency at which the system operates as well as the range of movement of member 43. In general, however, it may be determined by simple experiment and may be varied within limits. Cooperating with the end of the variable guide is fixed guide 68' having at its end a fixture 'l2 consisting of a block of metal with a circular choking slot 13. This fixture 12 with its slot 13 is a forni of choking ange disclosed and claimed in the co-pending application o f Winfield W. Salisbury previously referred to. yIn this application, various forms of choke couplings are disclosed. In one form the couplings are bolted together, while in other forms a slight space between couplings may be tolerated. Thus in Fig. 10 the spacing between the end of wave guide 68 and its fixture 12 from the movable wave guide is determined by the teachings of the above application and provides the necessary mechanical structure for a transition between movable and stationary elements. Choke slot 13 is circular as shown in Fig. 11 and so disposed that the bottom is alined with fixed choke 42 while the top is intermediate the two extreme positions of choke slot 45 during the movements of member 43.

By virtue of the construction shown in Figs. 10 and 1l, a sort of transformer impedance coupling is obtained. Thus the more-or-less fixed wave guide is coupled with the variable width guide over the range of variation. While the coupling may vary within the range of variation of the variable guide, the variation is not serious.

A simplified system Fig. 12 shows a simplified system mostly in block diagrams. It is understood that unless otherwise specified the system in general contains components which are common to radar systems. Thus the entire system may be pulsed by any suitable means, such means being either incorporated in the transmitter or receiver or may be a separate circuit indicated in the drawing as a timer. Inasmuch as systems of this character are pulsed at frequencies of between 500 and 2000 per second, it is clear that the source of timing may be any oscillator having such a pulse repetition frequency. Thus the oscillator may be either a sine wave oscillator or a multivibrator generating substantially rectangular waves at this frequency.

An example of a sine wave oscillator which is particularly stable and useful for this purpose vis the so-called Wien resistancecapacitance scillator, an example of which is disclosed on page 505 of Radio Engineers Handbook, by Terman, 1943 edition. An example of a multivibrator suitable for operation is shown on page 512 of this same book.

In order to utilize the timer and in accordance with well known practice, it is necessary to produce a sharp pip having a denite phase relationship with the original timer output. In the event that the timer oscillator generates sinusoidal waves, it is possible to pass the output through a distortion amplifier and generate square waves and thereafter peak the output and suppress undesired pips. the rectangular voltage output may be operated upon directly by a peaker and similarly used. Examples of such operation are disclosed in pages 177 to 180 of Ultra High Frequency Techniques, by Brainerd, Koehler, Reich and Woodruff, published in 1942.

The pips from the timer may be applied to the transmitter so that the latter is operated at proper intervals. The transmitter itself may be of the usual type adapted to generate a pulse of high frequency energy. This pulse of high frequency energy is communicated to the antenna system 'l5 by suitable connections such as wave guides, coaxial lines or open wire lines, in accordance with well known practice. While the transmitter is on, it is necessary to desensitize the receiver or disconnect the receiver from the antenna, and to this end a suitable switching means may be provided for accomplishing this. The receiver as shown may be connected to the same antenna system 'I5 or to another antenna if so desired, and the connection between the receiver and common antenna system I5 may include automatic switching means of the type well known in this art whereby during the time that the transmitter is on, the receiver is effectively cut 01T. Such switches may also provide as an additional feature the cutting oi of the transmitter from the antenna during the time that the receiver is to operate between pulses. If desired, the receiver may have suitable means for desensitizlng the same during transmitter operation, such means being adapted to be triggered by a pulse from the timer, and to this end the timer may have a suitable connectionv to the receiver.

Coincident with the triggering of the transmitter, it is necessary to initiate a sweep. As shown here, a sweep generator is triggered by the timer. It is understood, however, that this is merely exemplary and in practice it is possible to trigger the sweep generator from the transmitter or any other portion of the system in accordance with usual practice. The sweep generator may be of any suitable type such as shown l on page 515 of the book by Terman previously referred to or on pages 183 and 186, inclusive, and pages 218 to 220, inclusive, of Ultra High Frequency Techniques or in Figs. 27 and28 herein.

It is well known that either electrostatic or electromagnetic deflection sweeps may be used, and the change from one to the other isunderstood by those skilled in the art. For convenience and simplicity, an electrostatic sweep is herein disclosed. It is understood, however, that each pair of deecting plates may be replaced by a pair of magnetic defiecting coils, and the only change necessary in the circuits will be to provide for the initial voltage to overcome the inductance and thereafter provide for current variation rather than voltage variation.

The output of the linearLV sweep generator may be designated as 1 sinceitv corresponds to the range of the system,A and this output is fed in part to a scan potentiometer. TES scan potentiometer is adapted to operate uponto vary its magnitude in accordance with the sine of angle of scan. While various means for obtaining a sinusoidal change of voltage are known, a simple means may be provided asshown. Thus, the output of the linear sweep generator may be fed to a resistance It over which a potentiometer With a multivibrator,

audace wiper 11 is adapted to operate. This wiper may' be carried on bar 18 having cam roller 19 springpressed against suitably shaped cam 80 driven by scan motor 34. It is understood, of course, that cam 80 is shaped and operates in time relation so that the potential of wiper 11 with respect to ground, or any other suitable reference point, is varied in accordance with the sine of the scan angle.

The potential taken from wiper 11 is thus r sin a and may be impressed upon a suitable amplifier 8|. An example of such an amplifier for an electrostatic type of cathode ray tube is shown on page 225 of Ultra High Frequency Techniques. Other amplifiers well known for this type of work may be used. In the event that the cathode ray tube is of the electromagnetic type, other circuits described in this book, such as on page 502, may be used. The output of amplier 8| may be applied through a reversing switch lila to the deilecting electrodes of a cathode ray tube 82, such deflecting electrodes in this instance being the horizontal plates 83 and 84 of an electrostatic type of tube. Thus the :c component of sweep may be provided.

In order to get the y component of the sweep in cathode ray tube 82, the output of the linear sweep generator is also fed to a ril-2:2 circuit 86 shown in a block but explained in detail later. The output of circuit 86 is fed to another circuit described as r2-x2-h2 and indicated by numeral 81. In circuit 81, which is shown in detail later, the component h2 corresponding to the square of the altitudev is added to the r2-.r2 of circuit 86. The -hz voltage may be obtained in any suitable manner either by manual means, since the variation of altitude may be relatively slow, or by automatic means.

Thus one automatic means is shown and includes a Sylphon bellows 90 anchored to a base 9|. Sylphon bellows 90 is well known as a ilexible, sealed, metal container which may be suitably evacuated and supported by a spring inside to prevent collapse. Such a bellows will respond to variations in atmospheric pressure and in various forms are used in aneroid barometers. Thus bellows 90 may be carried in a plane in such a manner that the outside of this bellows is exposed to .the atmosphere and when properly calibrated may be used to determine height accurately. The movable end 92 of bellows 90 may carry a rod 93 which is pivotally secured to another rod 94 pivoted at 95 to any fixed point and insulatingly carrying a potentiometer wiper 96. A spring 91 controlled by a thumb screw 98 may be used to calibrate the device. If desired, a suitable indicator cooperating with a scale may also be provided so that altitude may be read directly. However, such altimeters are well known in the art and need not be described.

Potentiometer wiper 96 cooperates with potentiometer resistance winding having one end grounded and the other end connected through load resistor |0| 'to a suitable source of potential. Wiper 96 is connected by lead |02 to high resistance |03 having its otherend grounded. Thus the potential existing across resistance |03 is proportional to h or altitude of the aircraft. It is understood that resistance |03 is high in comparison to potentiometer resistance |00 so that the accuracy of the potentiometer is not seriously impaired. At two points on resistance |03, such as points |04 and |05, connections are taken ofi' to a pair of grids |06 and |01 of a vacuum tube |08. This vacuum tube is of the tetrode type and has a cathode |09 connected to ground through a load resistor |40 and thus operating as a cathode follower. Anode of this tube may be connected to a suitable source of potential such as B+ shown. y

The potentials applied to grids |08 and |01 have such a relation in comparison to the amplication control of these grids that the final effect of one grid on the vacuum tube is the same as the other grid. Thus if grid |06 requires twice the voltage that grid |01 requires for the same effect on the space current, then points |04 and |05 on resistors |03 are so chosen as to maintain this relationship. This eiect of both grids |06 and |01 must be multiplied in accordance with well known vacuum tube practice to obtain the output eiect so that by proper design of the resistors |02 and proper choice of points |04 and |05, the current through yvacuum tube |08 may be varied in accordance with the square of h. Hence the potential across cathode load resistor IIO will also vary directly as the square of the altitude. In place of a cathode follower, a conventional plate load resistor may be provided in which case the variation will be negatively as the square.

In place of this electrical system for obtaining a voltage in proportion to the square of the altitude, it is possible to have Sylphon 90 move arm 94 and wiper 96 over a specially wound potentiometer having non-uniform resistance so that a linear movement of the arm will result in a proper variation of altitude. Other methods involving the use of cams may also be used.

The output of circuit 81 is then fed to a square root circuit H2, also to be explained in detail later, and this output may then be fed to an amplifier ||3 which may be similar to amplifier 8|. Amplifier ||3 may feed vertical deflection plates I4 and ||5 of the cathode ray tube. Thus the y component of the beam deflection is now provided.

The showing of connections between the amplifiers and deflecting plates is diagrammatic. In practice, additional amplifiers may be necessary and beam centering controls for both sets of deecting plates would be provided as shown, for example, on pages 223 to 225, inclusive, of Ultra High Frequency Techniques previously referred to.

In order that targets may be indicated on the screen of tube 82. means may be provided whereby the beam is normally suppressed, but upon the occurrence of a target echo in the receiver, line H6 from the receiver feeds a positive target echo pulse to control grid l l1 of a cathode ray tube to produce a momentary intensification of the beam. Other methods for intensifying the target echo may be provided.

Referring now to Fig. 13, there are shown some circuits elaborating on the block diagram of Fig. 12. Thus the linear sweep generator feeds its output r to potentiometer 16. Wiper 11 is moved over this in accordance with the rotation of cam so that the potential at wiper 11 corresponds to r sin a. The potential at wiper 11 is fed-through a suitable lead |20 for use as the :r control of cathode ray tube 82. It is understood, of course, that this output is suitably amplified in amplifier 8|, as previously referred to.

The potential at wiper 11 is also applied through an isolating cathode follower stage to potentiometer |22. In this, as in other similar instances it may be desirable to isolate one potentiometer from another as far as current flow is concerned. This is for the purpose of preventing distortion in potentiometer characteristics due to the creation of parallel resistance paths. A cathode follower stage may be used since the grid can be so biased as to draw no current. Furthermore phase inversion is avoided and loss of ampliiication may be made-up later. In this instance, wiper 11 goes to grid 11a of a vacuum tube 11b whose anode 11e may be connected to a suitable source of B+ potential. Cathode 11d is connected to potentiometer |22, over which a wiper |23 plays.

Wiper |23 moves with wiper 11 so that the potential of wiper |23 with reference to the potential across resistance |22 is multiplied by sin a. Thus the output at wiper |23 has a value corresponding to r sin a or since :c is equal to r sin a, then the output is equal to :r sin a. This output may be applied through an isolating stage to cathode load resistance |24. Thus wiper |23 is connected to grid |23a of vacuum tube |23b whose anode |23c is connected to B+. Cathode `|23d is connected to load resistance |24 which resistance may also be connected to cathode 25 of vacuum tube amplifier |26. In the event that the potential at cathode |25 is too high for convenient amplifier use (due. to cathode follower action), it is understood that cathode |25 may be connected to a point on resistance |24 nearer ground. Vacuum tube |26 has its control grid |21 connected to the output of the sweep generator so that a voltage r is effectively applied thereto. Amplifier i 26 has its anode |28 connected to a cathode |30 of a vacuum clamping tube |3|, whose anode |32 is connected to a suitable source of B+ potential. Vacuum tube |3| has its control grid |34 connected to a source |35 adapted to supply a negative square gate shown during the time that the sweep is to make a complete journey.

Just when the sweep starts, which may be when the transmitter begins to operate, a negative gate is applied to grid 34, this negative gate being sufcient to drive tube |3| to cuto. The duration of this negative gate is sumcient to accommodate the longest range of the system and this naturally will be less than the complete time interval between successive transmitter pulses. It is understood that in the event that an electromagnetic type of control is used on the cathode ray tube,

some time displacement between the transmitter pulse and the sweep may be necessary. Thus it is customary to start electromagnetic sweeps slightly ahead of the transmitter pulse so that the edects of inductance may be overcome and the actual generation of beam controlling field may be initiated at the same time as the transmitteris operating. This, however, is well known in the art and no detailed description is necessary.

The gate may be supplied by a biased multivibrator triggered from the timer. Such a multivibrator is illustrated on page 1'16 of Ultra High Frequency Techniques referred to above.

Connected across the cathode and anode of vacuum tube |3| is a condenser |36. From the cathode terminaly of condenser |36, a coupling condenser |31 is connected to control grid |38 of a vacuum tube amplier |39. Control grid 38 may have its grid circuit completed by a suitable resistor to ground while cathode 4| of the vacuum tube is provided with a suitable bias resistor |42 to ground. Tube |39 has its anode |43 connected through a load resistance |44 back to the B+ lead. Anode |63 is also connected to a potentiometer |45 across which is connected a suitable source of potential |46, here shown as a battery but which may be any suitable source with the polaritles as indicated, namely the negative polarity immediately adjacent anode |43. Cooperating with potentiometer winding |45 is a wiper |48 whose position is controlled by a suitable control mechanism diagrammatically shown as |50. which is adapted to set wiper |48 in accordance with the square of the altitude of the plane. Such mechanism may be Sylphon actuated as shown in Fig. 12 and provided with a suitable cam arrangement to square the altitude.

Potentiometer wiper |48 is connected back to anode |43 through a condenser |50 and is also connected to the positive terminal of a suitable source of potential |5|, here diagrammatically shown as 'a battery. The negative terminal of potential source |5| is connected down to control grid |53 of Vacuum tube |54 whose cathode |55 is grounded through a suitable bias resistor |56. Tube |54 has its anode |51 connected through load resistor |58 to lead |50 going to a suitable source of B+ potential. Another vacuum tube |60 has its cathode |6| connected to cathode |55 of tube |54 while its control grid |62 is connected to anode |63 of a pentagrid tube and thence through a suitable load resistor |64 to the B+ terminal. Tube |60 has its anode |65 connected through load resistor |66 to wire |58 while the anode itself is connected through condenser |61 to two seriesconnected resistances |88 and |68. An intermediate point |10 ,between these resistors is grounded while the end terminal of resistance |69 is connected through a condenser |12 back to anode |51 of tube |54.

Resistance |68 also has its terminal connected vby lead |13 to No. 1 and No. 3 grids |14 and |15 iiection potentials to the cathode ray tube.

A suitable reversing switch is provided in the leads giving the :c deflection so that when the scan angle a is positive, the sweep is applied in one direction and when the scan angle is negative, the sweep is applied in the reverse direction. Thus in Fig. 12, a reversing switch in the leads to plates 83 and 6| is provided, said switch being actuated by scan motor 3ft just when the scan angle changes, namely when reflecting member 21 of Fig. 5 is turned.

The operation of the circuit of Fig. 13 will now be explained. is has been previously pointed out, there is impressed upon cathode |25 of vacuum tube |26 a bias potential which is eiiectively proportional to x sin a. 0n the control grid of this tube there is impressed a potential which is proportional to 1*. Ordinarily, vacuum tube |3| functions as a clamping tube to short circuit condenser |36 and normally retain anode |28 of vacuum tube |26 at a xed potential. Upon the occurrence of a negative gate at terminal |35, vacuum tube |3| is cutoff and condenser |36 begins to charge. The current through condenser |36 will be controlled by the space current passing through tube |26. This space current will be proportional to the difference between the grid potential r and the cathode potential a: sin a or r sin2 a. It is understood that the polarity of 

